Ookinesis in Cerebratnlus Lacteiis. 381 



Interzonal fibers- — fibers found between the separating chromo- 

 somes at the anaphase and telophase. These should not be con- 

 founded with the spindle fibres exposed between two daughter chromo- 

 somal plates.^^ 



(b) Observations. 



Many views have hitherto been expressed as to the nature, forma- 

 tion and function of the rays and spindle, yet, when they are crit- 

 ically examined, what we actually know at present is surprisingly 

 little. Any attempt to formulate such a highly intricate mechanism 

 l)ased on the body of evidence we have at hand seems premature. 

 In the present section, therefore, 1 shall not go into the general dis- 

 cussion, but I shall confine myself to the description of a few ob- 

 servations, which have a direct bearing on this subject. 



As has been maintained by some cytologists, the rays, I think, 

 are physically modified hyaloplasm of fiuid consistency (^lark, '81, 

 p. 528; Wilson, 'Ola, pp. 54-1, 549; '01b, p. 385). The effect of 

 ether, cooling, etc., is to bring the rays quickly to the original 

 hyaloplasmic state. Evanescent as they may seem, the rays are, 

 under normal conditions, fairly persistent structures, as shown by the 

 fact that at the moulting of the centrosome the old rays linger for 

 a long while even after the central ends of the rays disappear. It 

 is extremely difficult, therefore, to conceive that the rays represent 

 raj)id constant currents of hyaloplasm as Teichmann ('03 j and Bon- 

 nevie ('06) maintain (Rhumbler, '96, p. 583). It might be men- 

 tioned in this connection that the pole rays of the first maturation 

 mitosis remain unchanged for three or four hours unless fertilizctl. 



In fixed material the rays may be divided into two classes accord- 

 ing to their nature: (a) fibrous, and (b) non-fibrous (Fol, '91,. 

 The former are actual fibers imbedded in hyaloplasm with micro- 

 somes attached to the surface. Tracing the fibrous rays peripherally, 

 one always finds straightened alveolar walls forming non-fibrous rays 

 or, as sometimes called, ''Dotterstrahlen."-" In Fig. 54 (PI. Ill) 



"All the filn'cs seen between the two danghter chromosomal plates, including 

 both the spindle and interzonal til>res, were called by Mark "interzonal tila- 

 ments" ("SI, p. 198). 



^The "Dotterstrahlen" of older writers simply mean rays, since the cytoplasm 

 was called "Dotter" in some cases. 



